esp8266-intexsbh20

• fixed compiler warnings (comparison of constant is always true, catching polymorphic type by value)
• fixed platform_packages option
• updated dependencies for GitHub Actions (Arduino Core for ESP8266 3.1.2, ArduinoJson 6.21.3)

• ESP8266 SDK 3.1.2
• ArduinoJSON 6.21.3

• move firmware code and config data into src folder
• fix compiler warnings
• updated README
• updated GitHub build action

optionally specify MQTT server port in config file

set desired water temperature without interrupting MQTT connection

changed data type of disinfection time setpoint from bool (on/off) to int (hours)

changed data type of actual disinfection time from bool (on/off) to int (hours)

• support more than 16 symbols per 7-segment display
• support reading disinfection time for model SJB-HS
• changed error code data type from uint32 to string to make it human readable

support both Intex PureSpa SB-H20 and SJB-HS models, selectable during build using a #define in source file common.h

add configuration option to choose MQTT retain setting (default: disabled)

support MQTT authentication with username/password